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/* origin: FreeBSD /usr/src/lib/msun/src/k_tanf.c */
/*
* Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
* Optimized by Bruce D. Evans.
*/
/*
* ====================================================
* Copyright 2004 Sun Microsystems, Inc. All Rights Reserved.
*
* Permission to use, copy, modify, and distribute this
* software is freely granted, provided that this notice
* is preserved.
* ====================================================
*/
#include "libm.h" // for __tandf
#include <math.h> // for double_t
/* |tan(x)/x - t(x)| < 2**-25.5 (~[-2e-08, 2e-08]). */
static const double T[] = {
0x15554d3418c99f.0p-54, /* 0.333331395030791399758 */
0x1112fd38999f72.0p-55, /* 0.133392002712976742718 */
0x1b54c91d865afe.0p-57, /* 0.0533812378445670393523 */
0x191df3908c33ce.0p-58, /* 0.0245283181166547278873 */
0x185dadfcecf44e.0p-61, /* 0.00297435743359967304927 */
0x1362b9bf971bcd.0p-59, /* 0.00946564784943673166728 */
};
float __tandf(double x, int odd)
{
double_t z, r, w, s, t, u;
z = x * x;
/*
* Split up the polynomial into small independent terms to give
* opportunities for parallel evaluation. The chosen splitting is
* micro-optimized for Athlons (XP, X64). It costs 2 multiplications
* relative to Horner's method on sequential machines.
*
* We add the small terms from lowest degree up for efficiency on
* non-sequential machines (the lowest degree terms tend to be ready
* earlier). Apart from this, we don't care about order of
* operations, and don't need to to care since we have precision to
* spare. However, the chosen splitting is good for accuracy too,
* and would give results as accurate as Horner's method if the
* small terms were added from highest degree down.
*/
r = T[4] + z * T[5];
t = T[2] + z * T[3];
w = z * z;
s = z * x;
u = T[0] + z * T[1];
r = (x + s * u) + (s * w) * (t + w * r);
return odd ? -1.0 / r : r;
}
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